If you are talking about the flow rate adjustment of medical O2 bottles, this won't work when you push O2 through a stone. To my understanding these flow rate meters assume that there is no back-pressure on the O2 output. But when you have pressure on the output b/c of a O2 stone the flow rate will be much less. In addition to that the pressure it takes to push O2 through a sintered varies very much from stone to stone.

If you have a flow rate meter like this, I'd think you'd be measuring the actual flow regardless of resistance:

If you have a medical regulator like this, then the resistance will affect the rate:

I don't know if this is that big of a deal, since you're only making a rough estimate anyways. Even if you know the exact rate, O2 that bubbles to the surface isn't being absorbed so higher rates are just a waste of money. Pick a moderate rate that produces minimal foam and stick with it, and you should be able to dial in your process by adjusting the time you run it for. Just like pitching rate, oxygenation is a variable that you can change to get a different result. If you like the way the beer turns out, you don't need a DO meter.

If you have a flow rate meter like this, I'd think you'd be measuring the actual flow regardless of resistance:

If you have a medical regulator like this, then the resistance will affect the rate:

I don't know if this is that big of a deal, since you're only making a rough estimate anyways. Even if you know the exact rate, O2 that bubbles to the surface isn't being absorbed so higher rates are just a waste of money. Pick a moderate rate that produces minimal foam and stick with it, and you should be able to dial in your process by adjusting the time you run it for. Just like pitching rate, oxygenation is a variable that you can change to get a different result. If you like the way the beer turns out, you don't need a DO meter.

You just told me YDIW! Something I had not thought of. Might have to go to a higher flow rate, or a longer time at a lower flow rate. Dang - always something to consider. No DO meter here.

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Jeff RankertAnn Arbor Brewers Guild, AHA Member, BJCP CertifiedHome-brewing, not just a hobby, it is a lifestyle!

I deal with flow meters in my work and I agree with Narvin that the Rotameter type (the clear tube one) shouldn't be too affected by back pressure. That type relies on the gas velocity through the tube and that velocity lifts the pellet to indicate flow rate. The minor increase in gas density due to back pressure should not significantly alter the accuracy of the flow measurement.

I deal with flow meters in my work and I agree with Narvin that the Rotameter type (the clear tube one) shouldn't be too affected by back pressure. That type relies on the gas velocity through the tube and that velocity lifts the pellet to indicate flow rate. The minor increase in gas density due to back pressure should not significantly alter the accuracy of the flow measurement.

+1 The rotameter gives a volumetric measurement. Back pressure will not affect it. Just need to make sure that the pressure going into the system is greater than your back pressure or you will get no flow.

What I like to a lot these days is to shoot some O2 into the headspace, seal it with a stopper and shake it well for 30 s. This gives me very reliable results. For lagers I have to do this twice to get to 12 ppm.

the only downside is the foam, which prevents you to add a lot of wort in which the yeast is suspended.